Science

http://channel.nationalgeographic.com/channel/human-footprint/consumption-interactive.html measure your human footprint.
http://www.sciencegeek.net/lingo
http://www.khanacademy.org/ a library with videos, and practice exercises covering everything from arithmetic to physics
http://sciencenetlinks.com/tools/ tools for teaching
http://www.solarsystemscope.com/scope.swf great interactive solar system
http://www.mathopenref.com/calculator.html math /science calculator
http://phet.colorado.edu/ Fun, interactive, research based simulations of physical phenomena from the PhET™ project at the University of Colorada
http://nlvm.usu.edu/en/nav/vlibrary.html National library of virtual munipulatives
http://cosmos4kids.com/ full of resources and visuals.